Coupled coil system



Sept. 24. 1940- E. A. VAN YZEREN COUPLED COIL SYSTEM Filed Oct. 4. 1938u 1 I 1 l I I I l l I z z z I l v INVENTOR EA. VAN YZEREN BY ATT RNEPatented Sept. 24, 1940 C'OUPLED o'oIL SYSTEM Ewoud Adriaan van Yzeren,Eindhoven, Netherlands, assignor, by mesne assignments, to RadioCorporation of America, New York, N. Y.', a corporation of DelawareApplication October 4, 1938, Serial No.- 233,181 In Germany February1.0, 1938 3 Claims.

This i'nvention relates to a coupled coil system comprising'at least onefixed and one movab'le coil more particularly for high-frequency'band-pass filters in which the inductive coupling of the coils isadjustable by varying the relative position of the coils and theadjustment of the coupling does not alter substantially the selfinduction of the coils.

A known coil system satisfying this condition comprises two disc-shapedcoils which are arranged so that the axis of the stationary coilperpendicularly intersects the axis of the movable coil substantially inthe coil 'centre of the last mentioned coil, the mo'vab'le coil beingmovable in the direiction of its aXs.

An important advantage of the Well-known arrangement is that the twocoils can be cou-pled very loosely or, if desired, can be completelydecoupled. I-lowever, it has 'been found that the well-known arrangementdoes not permit a compact construction. Indeed, if the coils are closelyapproached together the displacement required for modifying the couplingfactor by a definite amount is so slight that the adjustment of themovable Vcoil involves dificulties from a mechanical point of view. Inthis case easy and accurate adjustment of the couplng is no longerpossible. Moreover, mechanical vibrations or the like involveconsiderable variations of the adjusted coupling.

The present invention avoids these draW-'backs' whilst conserving theabove-mentioned advantages and consists in that the movable coil isarranged in the region of the strongest curvature of the lines of forceof the magnetic field produced by the stationary coil and is movablesubstantially iii the direction of the lines of force there available.

The movable coil is preferably arranged so that with the loosestcoupling the axis of the 'coil extends substantially perpendicularly tothe lines of force produced by the stationary coil. Furthermore the axesof the two coils preferably extend parallel with each other. If the axisof the movable coil extends normally to the lines of force themodification of the coupling obtained by a given displacement is amaximum.

If the coil system is surrounded by metal screenu ing means the movablecoil, according to a further feature of the invention, is arranged sothat the coupling decreases when the coil approaches the neghboring wallof the housing.

The nvention will 'be more clearly understood .'35 by reference to theaccompanying drawing.

(Cl. PiS- 44) Figure 1 represents diagrammatically a stationary and amovable coil.

, Figure 2 is a graph o-f the value of the coupling factor of the twocoils in accordance with the displacement of the movable coil. 5

In Fgure 1 the reference I designates a stationar'y coil and 2 a movablecoil each of which is provided with an iron core 3 and 4 respectively.The coils are screened 'by a metal housing. For the sake of clearnessthe mechanical attachment of the coils, which is not important for thepresent invention, has not been represented.

The lines of force of the magnetic field produced by the stationary coilare indcated by dotted lines 5. The movable lcoil 2 is located in theregion of the strongest curvature of these lines of force and its axisextends almost perpendicularly to the lines of force available at thispoint. T'he coil 2 is movable in the direction of the lines of forcethere available, as is indcated by arrows 6 and 1. In the illustratedposition of the mo-vable coil the coil-centre is at 8. At this point'the lines of force have an upwardly direct component which induces adefinite voltage on the coil 2. If, on the contrary, the 'coil islocated at IO the lines of force embraced 'by the co-il have a componentwhich is directed downwardly in the figure and =by which a voltage isinduced on the coil, which, if desired, has the same value but isoppositely directed. It will be appreciated that between the points 8and ll] there is a point 9 at which no voltage is induced on the -coil2, i. e., consequently that the two coils are then magneticallydecoupled. In the case of magnetic decoupling the axis of the movablecoil 2 will extend substantially perpendicularly to the lines of forceset up in the coil.

In Figure 2 the square of the coupling factor (K2) has 'been plotted inaccordance with .the displacement (d) of the movable coil 2 for the ar-40 rangement shown in Figure 1. The point from which the co-ordinatesoriginate has been chosen in accordance with the point 9 in Fgure 1. Thedisplacement (d in mms.) in the direction 6 on the abscissa-axis hasbeen plotted on the right-hand side and the displacement in the oppositedirection 'l on the left-hand side. The degree of the coupling factorwas chosen at will and plotted according to a logarithmc scale.Generally a co'mparatively small portion A, corresponding to adisplacement a, of the obtainalble adjustng range will 'be utilized. Asappears from Figure 2 an equally strong coupling can be obtained oneither side of the `po-int 9 at which the two coils are decoupledmagnetically. If there are no metal screening means for the coils, thecoil 2 may be located on one or on the other side of the point 9. If,however, metal screening means are provided it is advantageous to locatethe coil 2 at 8 since in this case the coil is as remote as possiblefrom the neighbouring wall of the housing; in this manner theneighbouring Wall of the housing only slightlyaffects the naturalinductvity of the coil 2 in case of a displacement As appears fromFigures 1 and 2 the coupling decreases if the movable lcoil approachesthe Wall of the housing.

What I claim is:

1. In a high frequency band-pass filter, a stationary and a movable coilarranged with their axes in spaced parallel relation, there being oneposition of adjustment 'of the mova'ble coil such that it is located inthe region of the greatest curvature of the lines of force of themagnetic field produced by |the stationary coil Whereby the coils aresubstantially in decoupled relation, the movable coil being adapted forlateral adjustment in either direction fro'm its first-mentionedposition for varying the degree of coupling between said coils.

2. In` a high frequency band-pass filter, a stationary and a movablecoil arranged one above the other and with their axes in spaced parallelrelation, a conductive shield surrounding said lcoils, there being oneposition of adjustment of the movable coil such that it is located inthe region of greatest `curvature of the lines of force of the magneticfield produced 'by the stationary coil whereby the coils arersu'bstantially in decoupled relation, the movable coil being adaptedfor lateral adjustment in either direction from its first-mentionedposition for varying the. degree of coupling between said coils, and forequal adjustments of the movable coil the degree of coupling 'being lessin the direction towards the adjacent side of the shield than in theopposite direction.

3. A high-frequency coupling device including a stationary and amova'ble inductor each having a coil and a magnetic core, a conductiveshield surrounding said inducto-rs, said inductors being positioned oneither side of the shield axis With their` axes parallel to each otherand to the axis of said Shield, and means for adjustin-g the movableinductor transversely of the axis of said shield Whereb'y the couplingbetween said inductors may be adjusted, the arrangement being such thatwith adjustment of the movable inductor toward the Shield wall, thecoupling first deoreases to a minimum and then increases 'but at adifferent rate of change.

EWOUD ADRIAAN VAN YZEREN.

